The present invention relates to an inkjet head printing device such as an inkjet printer having an inkjet head for ejecting ink to a recording medium.
The inkjet head printing devices have been widely used. Japanese Patent Provisional Publication No. HEI 4-341852 discloses one of conventional inkjet heads employed in the inkjet head printing device. The ink jet head has a fluid channel unit and an actuator unit. The fluid channel unit has a plurality of pressure chambers and a plurality of nozzles provided respectively for the plurality of pressure chambers. Ink introduced into the pressure chambers is ejected from the nozzles by applying pressure to the pressure chambers using the actuator unit. To form an image on a sheet of paper, pressure is selectively applied to the pressure chambers by the actuator unit.
The actuator unit has a laminated structure consisting of a plurality of piezoelectric sheets and a common electrode layer. Further, a plurality of small electrodes are formed respectively for the plurality of the pressure chambers on one of the piezoelectric sheets. The common electrode layer is maintained at a ground level. One of the piezoelectric sheets sandwiched between the common electrode layer and the plurality of small electrodes is used as an active layer that is distorted when voltage is applied thereto to apply presser to the pressure chambers.
If a voltage is applied between the small electrode and the common electrode, the voltage is applied to a portion of the piezoelectric sheet (i.e., the active layer) in a direction of polarization of the piezoelectric sheet. Therefore, the portion of the piezoelectric sheet expands/contracts in the direction of its thickness by a vertical piezoelectric effect, by which the volumetric capacity of the pressure chamber is changed and the ink is ejected from the nozzle.